<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    .box1 {
        width: 300px;
        height: 300px;
        border: 1px solid #c00000;
        position: relative;
    }

    .s1 {
        width: 30px;
        height: 30px;
        background: #000;
    }

    .s2 {
        position: absolute;
        width: 50px;
        height: 50px;
        background: #666;
        bottom: 0;
        right: 0;

    }
</style>

<body>
    <div class="box1">
        <div class="s1"></div>
        <div class="s2"></div>
    </div>
</body>

</html>